There are few protocols that incorporate 6-mercaptopurine at a dose level of 1.0-5.0 to the 3rd power mg/M other than those that have been used to treat acute lymphocytic leukemia in children and acute nonlymphocytic leukemia in adults. In such studies count suppression, nausea and vomiting and moderately severe mucositis and stomatitis have occurred. 6-mercaptopurine has not been tested clinically as a single agent in high doses with respect to its antitumor effect. The objective of this study is to examine the antitumor effect of high dose 6-mercaptopurine in a broad spectrum of disseminated refractory neoplastic diseases. This is a non-randomized study and all patients received high dose 6-mercaptopurine 1.0 to the 4th power mg/M per day given by rapid IV infusion on the first five days of each 21 day course. As of February, 1976, 20 patients have been entered into this study. There have been no complete responses and there have been no partial responses. Four patients, all who had breast cancer, had objective responses (a response less than a partial response), two patients, both with lung cancer, had stabilization or no change in their disease and they had four or more courses of therapy. None of the 20 patients entered on this study are alive at this time. Hematologic toxicity was uniformly severe with count suppression occurring in all patients; in addition, nausea and vomiting occurred in all patients as well as moderate to severe mucositis and stomatitis.